Method of manufacturing semiconductor device

ABSTRACT

The present invention relates to a method of manufacturing a semiconductor device using a substrate including an organic low dielectric constant film containing a silicon, a carbon, an oxygen, and a hydrogen, with a resist pattern being formed on an upper layer side of the low dielectric constant film. The method comprising: an etching step in which the low dielectric constant film is etched by a plasma; an ashing step following to the etching step, in which the resist pattern is ashed by a plasma that is rich in oxygen radicals in such a manner that a relative dielectric constant of the low dielectric constant film can become 5.2 or more; and a recovering step following to the ashing step, in which an organic gas is supplied to the low dielectric constant film so as to recovery a damage of the low dielectric constant film caused by the plasma.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.60/960,163 filed on Sep. 18, 2007, and Japanese Patent Application No.2007-174307 filed on Jul. 2, 2007. The entire contents of theseapplications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a technique used in a manufacturingstep of a semiconductor device, wherein, after an organic low dielectricconstant film that is an interlayer dielectric film is etched, a resistthereof is ashed, and then a damage of the low dielectric constant filmis recovered.

BACKGROUND ART

In a dual damascene step as a method of forming a multilayer wiringstructure in a semiconductor device, there are formed, in an interlayerdielectric film, a via hole through which a wiring of an upper layer anda wiring of a lower layer are connected, and a trench (groove) in whicha wiring of the upper layer is embedded. Copper as a wiring metal isembedded in these recesses.

In order to form the recesses such as via holes and trenches in theinterlayer dielectric film, an etching step is performed by a plasmaobtained from a process gas. Thereafter, a resist is ashed by a plasmaobtained from an oxygen gas or a carbonic dioxide gas.

With a view to accelerating a signal transmission, formation of aninterlayer dielectric film out of a material having a low relativedielectric constant has been studied. An SiCOH film is known as arepresentative low dielectric constant film.

However, in the above etching step and the above ashing step, the SiCOHfilm may be damaged by the plasma. In particular, in the ashing step,the SiCOH film may be seriously damaged because the SiCOH film is anorganic film, while an oxygen gas is used in the ashing step. To bespecific, electric properties of the SiCOH film may be considerablydeteriorated.

As shown in FIG. 10A, this damage is caused when a connection between Siand a methyl group (CH₃), which form the SiCOH film, is disconnected bythe plasma of an oxygen gas, so that the methyl group, which has beendisconnected from Si, is desorbed from the SiCOH film. On the otherhand, the silicon (Si) from which the methyl group has been disconnectedis prone to absorb moisture. Thus, the silicon takes therein moisture inan atmospheric air and in a process gas, or moisture generated by areaction between oxygen in the process gas and hydrogen in the methylgroup, resulting in further deterioration of the electric properties ofthe SiCOH film. Such a damage may invite various problems such as abroadening of a line width of a pattern after a wafer is washed, anincrease in relative dielectric constant, an increase in leak current,and a deterioration in reliability caused by the moisture absorption.

Thus, a process for recovering the damage is performed according to thefollowing manner. Namely, as shown in FIG. 10B, a silazane-containinggas including methyl groups is supplied to the SiCOH film so as to add,as shown in FIG. 10C, the methyl groups to the silicon from whichanother methyl group has been disconnected.

The ashing step is performed by using a parallel-plate type plasmaprocessing apparatus under a condition that a damage given to the lowdielectric constant film is restrained as much as possible. For example,a power to be applied to an upper electrode is set at about 300 W withrespect to a 8-inch semiconductor wafer (referred to as “wafer” below).When the process gas is made plasma with this low application power,oxygen ions are mainly generated. The ashing step is performed by meansof these oxygen ions.

However, as shown in FIG. 11, a surface part of a SiCOH film 100, inwhich molecules have become smaller because of the desorption of themethyl groups, provides a dense layer 101 of a higher density by anenergy of the oxygen ions included in the plasma of the oxygen gas.Since this dense layer 101 acts as a solid obstacle, it is difficult forthe silazane-containing gas having relatively larger molecules to bepermeated into the SiCOH film 100. Thus, as shown in FIG. 11, only asuperficial part of the dense layer 101 can be recovered by the recoveryprocess.

JP2005-251837A (particularly, claim 1 and section 0037) describes that,when a resist pattern on an upper layer side of an organic lowdielectric constant film is ashed, an application power to an upperelectrode is not more than 0.81 W/cm² per unit surface area of a wafer(an application power to the upper electrode with respect to an 8-inchwafer is not more than 255 W). However, this condition is an oxygen-ionrich condition, and thus the above problems cannot be solved.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances.The object of the present invention is to provide a method ofadvantageously recovering an organic low dielectric constant film whichhas been damaged by a plasma in an etching process and an ashingprocess.

The present invention is a method of manufacturing a semiconductordevice using a substrate including an organic low dielectric constantfilm containing a silicon, a carbon, an oxygen, and a hydrogen, with aresist pattern being formed on an upper layer side of the low dielectricconstant film, the method comprising: an etching step in which the lowdielectric constant film is etched by a plasma; an ashing step followingto the etching step, in which the resist pattern is ashed by a plasmathat is rich in oxygen radicals in such a manner that a relativedielectric constant of the low dielectric constant film can become 5.2or more; and a recovering step following to the ashing step, in which anorganic gas is supplied to the low dielectric constant film so as torecovery a damage of the low dielectric constant film caused by theplasma.

According to the present invention, the resist pattern is ashed bypurposely using the plasma that is rich in oxygen radicals, and thus thedamage degree of the low dielectric constant film caused by the plasmain the ashing step is made worse. However, this process can restrainformation of a dense layer on the low dielectric constant film, wherebythe organic gas can permeate deeply into the low dielectric constantfilm in the succeeding recovering step. Accordingly, a recovery ratio ofthe damage of the low dielectric constant film can be improved in theend.

Specifically, in a case of an SiCOH film, the ashing process isperformed such that a relative dielectric constant of the SiCOH filmbecomes 5.2 or more. In this case, the ashing process is performed undera radical-rich condition, so that formation of a dense layer can berestrained.

Alternatively, the present invention is a method of manufacturing asemiconductor device using a substrate including an organic lowdielectric constant film containing a silicon, a carbon, an oxygen, anda hydrogen, with a resist pattern being formed on an upper layer side ofthe low dielectric constant film, the method comprising: an etching stepin which the substrate is loaded into a plasma processing apparatus andthe low dielectric constant film is etched by a plasma; an ashing stepfollowing to the etching step, in which, by using a parallel-plate typeplasma processing apparatus, under a process pressure set at a valuebetween 1.33 Pa and 6.67 Pa, an oxygen gas is made plasma by applying apower for generating a plasma to an upper electrode in such a mannerthat the power for generating a plasma applied to the substrate on alower electrode is between 1.91 W/cm² and 3.18 W/cm² per unit-surfacearea of the substrate, and the resist pattern is ashed by the plasma ofthe oxygen gas; and a recovering step following to the ashing step, inwhich an organic gas is supplied to the low dielectric constant film soas to recovery of a damage of the low dielectric constant film caused bythe plasma.

Due to the performance of the ashing step stipulated in this invention,the ashing process is performed under the radical-rich condition, sothat formation of a dense layer on the low dielectric constant film canbe restrained. As a result, the organic gas can permeate deeply into thelow dielectric constant film in the recovering step, whereby a recoveryratio of the damage of the low dielectric constant film can be improvedin the end.

In addition, the present invention is a storage medium storing acomputer program operatable on a computer, wherein the computer programincludes steps for performing the method of manufacturing asemiconductor device having the above features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing an example of a plasmaprocessing apparatus used for performing an etching step and an ashingstep in one embodiment of a method of manufacturing a semiconductordevice according to the present invention;

FIG. 2 is a longitudinal sectional view of an example of a recoveryprocessing apparatus used for performing a recovering step in oneembodiment of the method of manufacturing a semiconductor deviceaccording to the present invention;

FIG. 3 is a plan view showing an example of a substrate processingapparatus to which the plasma processing apparatus shown in FIG. 1 andthe recovery processing apparatus shown in FIG. 2 are connected;

FIGS. 4A to 4C are cross-sectional views of a substrate for explainingsteps in one embodiment of the method of manufacturing a semiconductordevice according to the present invention;

FIGS. 5A to 5C schematic views for explaining states of a substratesurface during the recovering step in one embodiment of the method ofmanufacturing a semiconductor device according to the present invention;

FIGS. 6A and 6B are cross-sectional views for explaining states of asubstrate surface after the recovering step in one embodiment of themethod of manufacturing a semiconductor device according to the presentinvention;

FIG. 7 is a cross-sectional view showing a structure of a substrate usedin Experiment 1 of the present invention;

FIG. 8 is a cross-sectional view showing a structure of a substrate usedin Experiment 2 of the present invention;

FIGS. 9A and 9B are characteristic graphs showing data obtained inExperiment 2;

FIGS. 10A to 10C are schematic views for explaining a damage of aconventional organic low dielectric constant film caused by a plasma;and

FIG. 11 is a schematic view for explaining a conventional recovery stateof a damage caused by a plasma.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention is described below. The presentinvention is a method of performing a plasma process and a recoveryprocess to a semiconductor wafer (hereinafter referred to as “wafer”).An example of an apparatus for performing the present method isdescribed in the first place.

[Plasma Processing Apparatus]

At first, there is described an example of a parallel-plate type plasmaprocessing apparatus for performing an etching process and an ashingprocess to a wafer W, with reference to FIG. 1.

A plasma processing apparatus 10 includes: a process vessel 21 formed ofa vacuum chamber, a stage 30 located on a center of a bottom surface ofthe process vessel 21; and an upper electrode 40 disposed on an upperpart of the process vessel 21.

A vacuum exhaust system 23 including a vacuum pump and the like isconnected to an outlet port 22 formed in the bottom surface of theprocess vessel 21 through an exhaust pipe 24. A transfer port 25 for awafer W is formed in a wall surface of the process vessel 21. Thetransfer port 25 is capable of being opened and closed by a gate valveG. The process vessel 21 is grounded.

The stage 30 is composed of a lower electrode 31 and a support body 32that supports the lower electrode 31 from below. The stage 30 is locatedon the bottom surface of the process vessel 21 via an insulation member33. Disposed on an upper part of the stage 30 is an electrostatic chuck34 to which an electric voltage is applied from a high-voltage DC powersource 35. Thus, a wafer W is electrostatically absorbed on the stage30.

A temperature-adjusting flow path 37 through which a predeterminedtemperature-adjusting medium flows, is formed in the stage 30, so that atemperature of the wafer W can be adjusted to a desired temperature bythe temperature-adjusting medium.

In addition, a gas flow path 38 through which a heat-conductive gas suchas an He (helium) gas is supplied as a backside gas, is formed in thestage 30. The gas flow path 38 is opened at a plurality of positions inthe upper surface of the stage 30. These openings are communicated withthrough-holes 34 a formed in the electrostatic chuck 34.

The lower electrode 31 is grounded via a high-pass filter (HPF) 30 a. Aradiofrequency power source 31 a supplying a frequency of 2 MHz isconnected to the lower electrode 31 via a matching device 31 b. A focusring 39 is arranged along an outer periphery of the lower electrode 31so as to surround the electrostatic chuck 34. When a plasma isgenerated, the plasma is adapted to focus on a wafer W placed on thestage 30 through the focus ring 39.

The upper electrode 40 is formed to have a hollow shape. In a lowersurface of the upper electrode 40, there are formed, e.g., uniformly, anumber of holes 41 for supplying a process gas into the process vessel21 in a dispersed manner. Thus, a gas showerhead is structured. A gasintroducing pipe 42 as a gas supply path is connected to a center of theupper surface of the upper electrode 40. The gas introducing pipe 42passes through the center of the upper surface of the process vessel 21via an insulation member 27. The gas introducing pipe 42 is divergedinto five branch pipes 42A to 42E on an upstream side thereof. Thebranch pipes 42A to 42E are connected to gas supply sources 45A to 45Evia valves 43A to 43E and flow-rate control parts 44A to 44E,respectively. The gas supply sources 45A to 45E are, for example, a CF₄gas source, a CO gas source a CO₂ gas source, an O₂ gas source, and anAr gas source, respectively. The valves 43A to 43E and the flow-ratecontrol parts 44A to 44E constitute a gas supply system 46.

The upper electrode 40 is grounded via a low-pass filter (LPF) 47. Aradiofrequency power source 40 a, which supplies a frequency higher thanthat of the radiofrequency power source 31 a, is connected to the upperelectrode 40 via a matching device 40 b.

A radiofrequency supplied from the radiofrequency power source 40 aconnected to the upper electrode 40 is a radiofrequency for making aprocess gas into plasma. A radiofrequency supplied from theradiofrequency power source 31 a connected to the lower electrode 31 isa radiofrequency for applying a bias power to a wafer W so as to drawions in the plasma to a surface of the wafer W.

[Recovery Processing Apparatus]

Next, a recovery processing apparatus 50 is described with reference toFIG. 2. The recovery processing apparatus 50 includes a process vessel51 and a stage 52. Disposed in the stage 52 is a heater 52 a as aheating unit. The heater 52 a is connected to a power source 52 b, andis configured to heat a wafer W to, e.g., 50° C. to 200° C. The stage 52has an elevating means such as pins, not shown. By means of theelevating means, a wafer W can be transported between the stage 52 and atransfer means, not shown, through a transfer port 53 formed in asidewall of the process vessel 51. In addition, a plurality of pins, notshown, for supporting a wafer W are arranged on a surface of the stage52. Thus, a wafer W can be supported with a slight gap between the waferW and the surface of the stage 52, so that adhesion of particles to arear surface of the wafer W can be restrained. The reference character Gin FIG. 2 depicts a gate valve.

A plurality of, e.g., four diverged ends of a gas supply path 54 areopened to a lower surface of the process vessel 51 at an intervalcircumferentially equal to each other, so as to surround the stage 52. Acarburetor 55 is connected to the other end of the gas supply path 54.On an upstream side of the carburetor 55, there are connected, viaflow-rate controllers 56 a and 57 a, a TMSDMA (trimethyl silyl dimethylamine) source 56 and a nitrogen gas source 57, respectively. Thus,TMSDMA in a liquid state is vaporized by the carburetor 55, whereby aTMSDMA gas as an organic gas can be supplied into the process vessel 51with a nitrogen gas serving as a carrier gas. Alternatively, a pressurein the process vessel 51 is reduced, while a pressure of the TMSDMA inthe carburetor 55 is set higher than the pressure in the process vessel51, whereby the TMSDMA gas can be supplied into the process vessel 51not by a carrier gas but by a pressure difference between the pressurein the process vessel 51 and the pressure in the carburetor 55. Anexhaust path 56 is connected to a top wall of the process vessel 51 at aposition opposite to a wafer W placed on the stage 52. Connected to theexhaust path 56 is a vacuum pump 57 having a pressure-adjusting part,not shown.

[Overall Structure of Apparatus]

As shown in FIG. 3, the aforementioned plasma processing apparatus 10and the recovery processing apparatus 50 are structured as a part of asubstrate processing apparatus 60 which is a multi-chamber system. Thesubstrate processing apparatus 60 is simply described below. Thesubstrate processing apparatus 60 includes a carrier chamber 61, a firsttransfer chamber 62 of an atmospheric air, a load lock chamber 63, and asecond transfer chamber 64 of a vacuum atmosphere. The plasma processingapparatus 10 and the recovery processing apparatus 50 are hermeticallyconnected to the second transfer chamber 64.

The first transfer chamber 62 is provided with a transfer arm 65 as afirst transfer means for transporting a wafer W between the carrierchamber 61 and the load lock chamber 63. The second transfer chamber 64is provided with a transfer arm 66 as a second transfer means fortransporting a wafer W between the load lock chamber 63, the plasmaprocessing chamber 10, and the recovery processing apparatus 50.

The substrate processing apparatus 60 is equipped with a control part 2Aformed of a computer, for example. The control part 2A has a dataprocessing part formed of a program, a memory, and a CPU. The programincorporates commands for causing the control part 2A to send controlsignals to respective parts of the substrate processing apparatus 60 soas to perform steps described below. The memory has a domain in whichvalues of various process parameters such as a process pressure, aprocess temperature, a process period, a gas flow-rate, a power, and soon can be written. When the CPU executes the commands of the program,the values of these process parameters are read out, and control signalscorresponding to the parameter values are sent to the respective partsof the substrate processing apparatus 60. The program (which may beaccompanied with a program relating to an input operation of the processparameters and/or a display thereof) is generally stored in a storagepart 2B formed of, e.g., a flexible disc, a compact disc, a hard disc,or an MO (magnet optic disc), and is installed in the control part 2A.

[Layer Structure and Flow of Overall Process]

Next, respective processes performed by the substrate processingapparatus 60 including the plasma processing apparatus 10 and therecovery processing apparatus 50 are described. Described herein is acase in which an (n+1)^(th) circuit layer is formed as an upper layer onan n^(th) circuit layer which has been formed on, e.g., an 8-inch waferW as a substrate.

Firstly, an example of a semiconductor substrate (hereinafter referredto as “wafer” W), to which the method of manufacturing a semiconductordevice according to the present invention is performed, is describedwith reference to FIG. 4A. An n^(th) circuit layer has a structure inwhich a wiring 71 formed of a metal such as Cu is embedded in an SiCOHfilm 70 which is an interlayer dielectric film. On an upper part of then^(th) circuit layer, a cap film 72 and a barrier film 73 are stacked inthis order from below. The cap film 72 is a film for protecting thecircuit layer from a mechanical impact during a CMP process, forexample. The barrier film 73 is a film for restraining diffusion of Cubetween the upper and lower circuit layers. Although a barrier film forrestraining diffusion of the metal is also formed between the SiCOH film70 and the wiring 71, illustration and description thereof are omitted.

Stacked on an upper part of the barrier film 73 are an SiCOH film 74, acap film 75, a bottom resist film 76, an oxidation film 77, ananti-reflection film 78, and a photoresist mask 79 as a resist pattern,in this order from below. The photoresist mask 79 is patterned so as toform a via hole in the SiCOH film 74.

Next, processes to be performed to the above wafer W are described. Acourse of the wafer W in the substrate processing apparatus 60 isdescribed at first. When a carrier, which is a transfer vessel of awafer W, is loaded into the carrier chamber 61 from the atmospheric sidevia a gate door GT, the wafer W is loaded into the load lock chamber 63by the transfer arm 65 through the first transfer chamber 62. Then, thewafer W is transferred by the transfer arm 66 to the plasma processingapparatus 10 through the second transfer chamber 64. In the plasmaprocessing apparatus 10, the wafer W is subjected to an etching-processand an ashing process which are described below. After that, the wafer Wis taken out from the plasma processing apparatus 10 by the transfer arm66, and is transferred to the recovery processing apparatus 50. In therecovery processing apparatus 50, the wafer W is subjected to a recoveryprocess described below. Thereafter, the wafer W is returned to thecarrier through a route reverse to the loading route.

(Etching Process)

After the wafer W is horizontally placed by the transfer arm 66 on thestage 30 in the process vessel 21, the gate valve G is closed. Abackside gas is continuously supplied from the gas flow path 38, and atemperature of the wafer W is adjusted to a predetermined temperature.

The process vessel 21 is evacuated by the exhaust system 23 through theexhaust pipe 24, so that the inside of the process vessel 21 is held ata predetermined vacuum degree. After that, a process gas such as a CF₄gas is supplied from the gas supply system 46 at a predetermined flowrate. Subsequently, a radiofrequency of 60 MHz is supplied to the upperelectrode 40 with a predetermined power. Thus, the process gas is madeplasma. In addition, as a radiofrequency for biasing, a radiofrequencyof 2 MHz is supplied to the lower electrode 31 with a predeterminedpower. By this plasma process, the anti-reflection film 78 and theoxidation film 77 are etched.

Then, the supply of the radiofrequencies and the process gas is stopped,and the process vessel 21 is evacuated. Then, a CO₂ gas and a CO gas asprocess gases are supplied into the process vessel 21 at predeterminedflow rates, and radiofrequencies with predetermined powers are suppliedto the upper electrode 40 and the lower electrode 31. Thus, the processgases are similarly made plasma, and the bottom resist film 76 isetched.

Thereafter, the supply of the radiofrequencies and the process gases isstopped, and the process vessel 21 is evacuated. Then, a CF₄ gas as aprocess gas is supplied into the process vessel 21 at a flow rate of 100sccm, for example, and a pressure in the process vessel 21 is set at6.67 Pa (50 mTorr), for example. Then, powers supplied to the upperelectrode 40 and the lower electrode 31 are respectively set at 1000 Wand 100 W, whereby the process gas is made plasma. By supplying theplasma to the wafer W, the cap film 75 and the SiCOH film 74 are etched.As shown in FIG. 4B, due to the etching process, a hole 80 is formed inthe SiCOH film 74 so that a surface of the barrier film 73 is exposed.

At this time, the process gas does not include an oxygen gas. Thus, nodamage is generated by a plasma of oxygen in the SiCOH film 74. However,the SiCOH film 74 is slightly damaged by an energy of the plasma of theCF₄ gas. Thus, a damage layer 81 is slightly formed on a sidewall of thehole 80. As described above, the damage layer 81 is a layer resultingfrom the desorption of the organic substance that has been connected tothe silicon (Si) in the SiCOH film 74.

(Ashing Process)

Thereafter, the supply of the radiofrequencies and the process gas isstopped, and the process vessel 21 is evacuated. Then, an oxygen gas asa process gas is supplied into the process vessel 21 at a flow rate of300 sccm, for example, and a vacuum degree is adjusted to be set at 1.33Pa (10 mTorr) to 6.67 Pa (50 mTorr), for example. Then, a power of,e.g., 600 W (1.91 W/cm²) to 1000 W (3.18 W/cm²) is supplied to the upperelectrode 40, so that the oxygen gas is made plasma. At the same time, apower of, e.g., 100 W (0.32 W/cm²) to 300 W (0.95 W/cm²) is supplied tothe lower electrode 31. Thus, the oxygen gas is activated and madeplasma, so as to thereby generate oxygen ions and oxygen radicals. Atthis time, since the plasma density is increased by adjusting theprocess condition as described above (raising the process pressure, andraising the power to be supplied to the upper electrode 40), an oxygenion concentration in the plasma is considerably decreased, while aradical concentration is increased. Further, since the power to besupplied to the lower electrode 31 is lowered as described above, theoxygen ions are not intensively attracted to the wafer W, but theradicals which have been generated in large quantity flow toward thewafer W.

When such a plasma is supplied to the wafer W, as shown in FIG. 4C, thebottom resist film 76 which is an organic film is ashed and removed. Inaddition, when the sidewall of the SiCOH film 74 (side surface of thehole 80) is exposed to the plasma, an organic substance such as a methylgroup is desorbed from the inside of the film. Due to the desorption ofthe methyl groups, a dangling bond that is highly active (reactive) isgenerated in Si in the SiCOH film 74. Moisture slightly contained in theprocess gas and/or moisture generated by a reaction between the oxygengas and hydrogen in the SiCOH film 74 is bonded with the dangling bond,so that an Si—OH bond is formed.

The oxygen plasma invades the inside of the SiCOH film 74 through voidsformed by the desorption of the methyl groups, so that methyl groupsinside the SiCOH film 74 are sequentially desorbed from the SiCOH film74, resulting in the formation of the damage layer 81. Oxygen ions wouldmake denser the damage layer 81 by an energy thereof. However, since theplasma formed under the above condition is poor in oxygen ions but isrich in oxygen radicals, the plasma is less likely to make denser thedamage layer 81. Thus, as shown in FIG. 5A, the damage layer 81 remainsporous with the voids formed by the desorption of the organic substancehaving been left as they are. As described above, when the plasma richin oxygen radicals is used, the increase in density of the damage layer81 can be prevented. Thus, since the oxygen radicals can permeate to theinside, the thickness of the damage layer 81 is increased (the depth ofthe damage layer 81 is increased), whereby a relative dielectricconstant is increased.

(Recovery Process)

Thereafter, the supply of the radiofrequencies and the process gas isstopped, and the process vessel 21 is evacuated. Then, the wafer W istaken out from the process vessel 21 by the transfer arm 66, and isloaded into the process vessel 51 of the aforementioned recoveryprocessing apparatus 50. On the stage 52, the wafer W is heated to apredetermined set temperature of, e.g., 150° C. Then, a TMSDMA gas issupplied at a flow rate of, e.g., 500 sccm, until a pressure in theprocess vessel 51 reaches 6.67 kPa (50 Torr), for example. After that,the supply of the TMSDMA gas is stopped, and the process vessel 51 isclosed to provide a closed space. This state is held for 150 seconds,for example.

The TMSDMA gas diffuses in the process vessel 51 and permeates thesurface of the wafer W so as to reach the hole 80 and further thesurface of the damage layer 81. As described above, since the damagelayer 81 is porous, the TMSDMA gas deeply invades the inside of thedamage layer 81 from the surface thereof, which is shown in FIG. 5B. Asdescribed above, the damage layer 81 is a part formed by the desorptionof the organic substance from the SiCOH film 74, and the silicon in thispart includes highly active dangling bonds. Meanwhile, the TMSDMA gashas reactive radicals such as methyl groups that have a weak bondingforce and thus can be easily desorbed from the TMSDMA gas. Thus, whenthe TMSDMA gas comes into contact with the silicon including thedangling bonds, the methyl groups are rapidly taken by the silicon.Further, the TMSDMA gas also acts on another silicon to which moisturehas been bonded. Specifically, the moisture is desorbed from the SiCOHfilm 74, and the methyl groups are bonded to the silicon from which themoisture has been desorbed.

When the methyl groups are sequentially brought from the TMSDMA gas tothe silicon, the concentration of the TMSDMA gas in the damage layer 81is decreased. The TMSDMA gas continuously diffuses inside the damagelayer 81, and the reaction between the silicon and the TMSDMA gasfurther proceeds. Thus, as shown in FIG. 5C and FIG. 6A, the recoveryprocess of the damage layer 81 is performed. (When the methyl groups aretaken out from the TMSDMA gas, a by product gas is generated. Sincemolecules of the by-product gas are small, the gas goes outside the hole80 through gaps between molecules forming the SiCOH film 74.)

Thereafter, the process vessel 51 is evacuated, and the wafer W is takenout from the process vessel 51. Then, a new resist pattern is formed,and a groove (trench), by which a wiring can be embedded in the SiCOHfilm 74, is formed by using this resist pattern. After Cu has beenembedded in a recess formed of the groove and the hole 80, a CMP processis performed. Then, as shown in FIG. 6B, an (n+1)^(th) wiring 82 isformed.

In the above embodiment, as the ashing process condition, the processpressure is set at a value between 1.33 Pa and 6.67 Pa, and the powersupplied from the upper electrode 40 is set at a value between 600 W(1.91 W/cm²) and 1000 W (3.18 W/cm²), in order to obtain a plasma thatis poor in oxygen ions and rich in oxygen radicals. The ashing processis performed to the exposed SiCOH film 74 by this plasma. Thus,formation of a dense layer with a higher density can be restrained atthe surface layer of the SiCOH film 74. Accordingly, the TMSDMA gas usedin the recovery process can deeply permeate into the damage layer 81,whereby a recovery ratio of the damage (recovery ratio of the electricproperties) can be enhanced. As a result, a semiconductor device havingfavorable electric properties can be obtained.

This embodiment can be explained in the following manner. That is tosay, conventionally, the ashing process is performed with an ashingprocess condition adjusted such that electric properties after theashing process are the best, and then the recovery process is performed.On the other hand, in this embodiment, based on an idea reverse to theconventional idea, by adjusting the ashing condition such that theproperties after the ashing process are worse as compared with theproperties after the conventional ashing process, the recovery ratio ofthe electric properties can be increased by the succeeding recoveryprocess.

To be specific, in the ashing process for the 8-inch wafer W, the powerto be supplied to, e.g., the upper electrode 40, which is a power forgenerating a plasma, is set at 600 W or more, so as to make worse theproperties of the SiCOH film 74 after the ashing process. As understoodfrom the below examples, the ashing process under this condition resultsin that the relative dielectric constant of the SiCOH film 74 becomes5.2 or more.

However, when the relative dielectric constant of the SiCOH film 74after the ashing process is excessively larger than 5.2, the damagerecovery ratio of the film in the subsequent recovery process isconsidered to be unsatisfactory. Specifically, it is not desirable thatthe relative dielectric constant of the film after the recovery processis over 3.2.

As clearly seen from the result of the below examples, by adjusting theashing condition as described above, an ashing rate can be raised. Thus,a throughput can be advantageously improved.

In order to prevent the invasion of the plasma into the hole 80, thepower to be supplied to the lower electrode 31 during the ashing processis preferably set at a value between 100 W (0.32 W/cm²) and 300 W (0.95W/cm²).

In addition to the TMSDMA gas, the gas used for the recovery processmay, be a DMC (dimethyl carbonate) gas as shown in the below examples.Alternatively, the gas may be another organic gas used in theconventional recovery process.

In addition, the film to which the ashing process and the recoveryprocess of the present invention are applied, is not limited to theSiCOH film 74, and may be a film containing Si, C, and O. In the aboveembodiment, when the recovery process is performed, the TMSDMA gas issupplied into the process vessel 51 until the pressure therein reaches6.67 kPa (50 Torr), and thereafter the supply of the TMSDMA gas isstopped. However, it is possible to adjust the pressure in the processvessel 51 at the above value by supplying thereinto the TMSDMA gassimultaneously with evacuating the process vessel 51 (it is alsopossible to adjust a flow rate and a volume of displacement of theTMSDMA gas).

Moreover, as the apparatus for performing the etching process and theashing process, there may be used a parallel-plate type of plasmaprocessing apparatus in which two frequencies are applied to a lowerelectrode. Further, the etching process and the ashing process may beperformed in separate chambers.

EXPERIMENT 1

Next, an experiment conducted for confirming the effect of the presentinvention is described. In the experiment, there was used, as shown inFIG. 7, an 8-inch (200 mm) wafer W in which an SiCOH film 91, anoxidation film 92, an anti-reflection film 93, and a photoresist mask 94were stacked in this order from below on an SiC film 90. A predeterminedrecess had been patterned in the photoresist mask 94.

Firstly, by using the wafer W, an experiment for seeking a processcondition that makes smaller the damage layer 81 was conducted.

After the etching process and the ashing process were performed in theaforementioned plasma processing apparatus 10, the recovery process wasperformed in the recovery processing apparatus 50. With respect to therespective process conditions, the etching process condition and therecovery process condition were unchanged, while the ashing processcondition was changed as shown in the below Table 1.

As Comparative Example 1-3, an experiment was conducted under an ashingprocess condition (conventional ashing condition heretofore used) whichmade best the state of the wafer such as electric properties after theashing process. In addition, as Comparative Example 1-4, an experimentwas conducted under the same condition as that of Example 1-2, exceptthat a power to the upper electrode 40 was set at 1500 W in the ashingprocess, and that a DMC (dimethyl carbonate) gas was used as a processgas for the recovery process.

The respective wafers W, which had been subjected to the recoveryprocess, were immersed into a hydrofluoric acid solution of 5% byweight. The aforementioned damage layer 81 will be dissolved in thehydrofluoric acid, while the SiCOH film 91 will be resistant to bedissolved in the hydrofluoric acid. Taking advantage of these phenomena,a quantity of the damage layer 81 was evaluated by measuring a width ofthe recess which had been broadened by the immersion of the wafer intothe hydrofluoric acid. The width of the recess was measured by observingthe cross section of the wafer W by an SEM with the enlargement ratio of150 k times.

The respective process conditions were as follows.

(Etching Process Condition)

Etching of Anti-reflection Film 93

-   -   Process pressure: 6.67 Pa (50 mTorr)    -   Power of upper electrode 40: 1000 W    -   Power of lower electrode 31: 100 W    -   Process gas: CF₄ gas=100 sccm    -   Process period: 70 seconds

Main Etching

-   -   Process pressure: 6.67 Pa (50 mTorr)    -   Power of upper electrode 40: 1200 W    -   Power of lower electrode 31: 1700 W    -   Process gas: CF₄ gas/Ar gas/N₂ gas=5/1000/150 sccm

Process period: 25 seconds

(Ashing Process Condition)

Process gas: O₂ gas=300 sccm

TABLE 1 Power of Power of Process upper lower Process pressure electrode40 electrode 31 period Pa (mTorr) W W sec Example 1-1 6.67 (50) 600 10036 Example 1-2 6.67 (50) 1000 100 34 Comparative 6.67 (50) 1500 100 29Example 1-1 Comparative 13.33 (100) 1500 100 36 Example 1-2 Comparative1.33 (10) 300 300 42 Example 1-3 Comparative 6.67 (50) 1500 100 34Example 1-4

(Recovery Process Condition)

-   -   Process pressure: 6.67 kPa (50 Torr)    -   Process gas: TMSDMA gas=500 sccm    -   Process period: 150 seconds    -   Temperature for heating wafer W: 150° C.

(Experiment Result)

The experiment result is shown in Table 2.

TABLE 2 Increase in width of recess (quantity of Ashing rate damagelayer 81) nm nm/min Example 1-1 16 715.5 Example 1-2 16 763.8Comparative 28 887.1 Example 1-1 Comparative 34 717.1 Example 1-2Comparative 14 610.5 Example 1-3 Comparative 23 763.8 Example 1-4

The result shows that the damage layer 81 was deteriorated inComparative Examples 1-1, 1-2, and 1-4.

In Examples 1-1 and 1-2, the ashing rate was improved as compared withthat of the conventional condition (Comparative Example 1-3).

From the above result, it was understood that, when the power suppliedto the upper electrode 40 was increased to a range between 600 W and1000 W, the seeming quantity of the damage layer 81 was close to thequantity of the damage layer 81 formed by the conventional method inwhich the power supplied to the upper electrode was 300 W, while theashing rate was improved.

When the power of the upper electrode 40 is increased, it is consideredthat the oxygen ion concentration in the plasma is decreased, asdescribed above. However, from the result shown in Table 2, it can besaid that, when the power is increased at as large as 1500 W, the damagecaused by the oxygen radicals are so serious that the damage cannot berecovered by the next recovery process.

Similar to the TMSDMA gas, it was found that the quantity of the damagelayer 81 was decreased by using the DMC gas (Comparative Example 1-4).

Further, with respect to Examples 1-1 and 1-2 and Comparative Example1-3, the etching process and the ashing process were conducted, and thenthe hydrofluoric-acid immersion test was conducted without performingthe recovery process. The quantities of the damage layer 81 were 26 nm,30 nm, and 22 nm, respectively. From this result, it was understoodthat, in Examples 1-1 and 1-2, although the seeming quantity of thedamage layer 81 was increased after the ashing process, the quantity ofthe damage layer 81 was recovered to a level close to the quantity ofthe damage layer 81 in Comparative Example 1-3 (supply power to theupper electrode 40 was 300 W).

A film reduction of the SiC film 90 was confirmed, but no difference wasfound between the wafers.

EXPERIMENT 2

Next, an experiment for evaluating electric properties was conducted. Asshown in FIG. 8, an SiCOH film 95 having a relative dielectric constantof 2.4 was deposited as a blanket film on an 8-inch wafer W for theexperiment, and the etching process, the ashing process and the recoveryprocess were performed to the wafer W. Excluding the followingconditions, the respective process conditions were unchanged from theconditions in Experiment 1. For comparison, samples were manufactured byperforming the etching process and the ashing process, but withoutperforming the recovery process.

Following thereto, a relative dielectric constant, a leak current, amoisture content, and a carbon amount were measured. For comparison, theelectric properties except for the leak current were similarly measuredwith respect to the samples which had not been subjected to the recoveryprocess. In addition, the electric properties of a wafer W before itunderwent the experiment (after the SiCOH film 95 was deposited) weresimilarly measured (Reference).

Publicly known methods were used for the measurement for the relativedielectric constant and the leak current (details of which are omitted).

In the measurement of the moisture content, the moisture content wasobtained by integrating the amount of moisture desorbed from the wafer Wwhen a temperature of the wafer W was increased to 100° C. to 500° C.,in accordance with a TDS (thermal desorption spectroscopy).

In the measurement of the carbon amount, a ratio of the carbon amountrelative to the silicon amount in the film was calculated in accordancewith an XPS (x-ray photoelectron spectroscopy). In addition, at thistime, the wafer W was spattered, and there was confirmed how the carbonamount was changed in the depth direction of the wafer W depending onthe duration of the spattering period.

(Etching Process Condition)

-   -   Process pressure: 10.0 Pa (75 mTorr)    -   Power of upper electrode 40: 1500 W    -   Power of lower electrode 31: 100 W    -   Process gas: CF₄ gas/Ar gas=80/160 sccm    -   Process period: 10 seconds

(Ashing Process Condition)

Example 2-1: the same as Example 1-1 except for the process period whichwas set at 25 seconds

Example 2-2: the same as Example 1-2 except for the process period whichwas set at 23 seconds

Comparative Example 2: the same as Comparative Example 1-3 except forthe process period which was set at 29 seconds

(Experiment Result)

Results of the relative dielectric constant, the leak current, and themoisture content are shown in Table 3.

TABLE 3 Relative Leak current dielectric A/cm2 Moisture constant @1MV/cm Content Before Example 2-1 5.2 — 7.60E−08 recovery Example 2-26.14 — 7.10E−08 process Comparative 4.11 — 8.90E−08 Example 2 AfterExample 2-1 2.90 2.10E−09 3.98E−08 recovery Example 2-2 2.93 5.60E−093.87E−08 process Comparative 2.84 1.77E−08 4.17E−08 Example 2Not-processed Reference 2.24 5.82E−10 2.00E−08 (Reference)

Before the recovery process, in Examples 2-1 and 2-2, the relativedielectric constant was increased (deteriorated) as compared with thatof Comparative Example 2. However, due to the performance of therecovery process, the relative dielectric constant was lowered, i.e.,improved to substantially the same degree as that of Comparative Example2 (conventional process condition).

On the other hand, as compared with Comparative Example 2, the leakcurrent and the moisture content were improved by performing therecovery process. In particular, the leak current is considerably (aboutone tenth) decreased.

From the above result, it was understood that, according to the methodof the present invention, the electric properties were remarkablyrecovered, which cannot be confirmed from the evaluation of the seemingquantity of the damage layer 81 in the above Example 1.

The peak position of moisture (heating temperature at which the peakbecomes the largest) obtained by the TDS differed between Examples 2-1and 2-2 and Comparative Example 2. From this point, it is consideredthat an adsorption factor (adsorption state) of moisture or a depth ofthe damage layer 81 (depth to which the moisture adheres) differedbetween Examples 2-1 and 2-2 and Comparative Example 2.

Next, the measurement result of the carbon amount is shown in FIGS. 9Aand 9B. In Example 2-2, by performing the ashing process, the damagelayer 81 extended deeply inside the wafer W, and the carbon amount wasdecreased. However, due to the performance of the recovery process, theTMSDMA gas invaded the inside of the wafer W, so that a distinguishablyhigh recovery ratio could be obtained.

The reason therefor is considered as follows. Namely, as describedabove, since the amount of oxygen ions is made smaller while the amountof oxygen radicals is made larger in the plasma used for the ashingprocess, no dense layer is formed on the damage layer 81. Thus, therecovery process is performed to the damage layer 81 in which the voidsremain.

On the other hand, in Comparative Example 2, it was understood that,although the damage layer 81 at the ashing process did not extend deeplyinto the wafer W, the carbon amount was not remarkably recovered by therecovery process.

The reason therefor is considered as follows. Namely, since a denselayer is formed by the energy of the oxygen ions on the damage layer 81positioned on the surface of the wafer W, the dense layer serves as asolid obstacle and makes it difficult for the TMSDMA gas to diffuse inthe wafer W.

In FIGS. 9A and 9B, the result of Experiment 2-1 is omitted.

1. A method of manufacturing a semiconductor device using a substrateincluding an organic low dielectric constant film containing a silicon,a carbon, an oxygen, and a hydrogen, with a resist pattern being formedon an upper layer side of the low dielectric constant film, the methodcomprising: an etching step in which the low dielectric constant film isetched by a plasma; an ashing step following to the etching step, inwhich the resist pattern is ashed by a plasma that is rich in oxygenradicals in such a manner that a relative dielectric constant of the lowdielectric constant film can become 5.2 or more; and a recovering stepfollowing to the ashing step, in which an organic gas is supplied to thelow dielectric constant film so as to recovery a damage of the lowdielectric constant film caused by the plasma.
 2. A method ofmanufacturing a semiconductor device using a substrate including anorganic low dielectric constant film containing a silicon, a carbon, anoxygen, and a hydrogen, with a resist pattern being formed on an upperlayer side of the low dielectric constant film, the method comprising:an etching step in which the substrate is loaded into a plasmaprocessing apparatus and the low dielectric constant film is etched by aplasma; an ashing step following to the etching step, in which, by usinga parallel-plate type plasma processing apparatus, under a processpressure set at a value between 1.33 Pa and 6.67 Pa, an oxygen gas ismade plasma by applying a power for generating a plasma to an upperelectrode in such a manner that the power for generating a plasmaapplied to the substrate on a lower electrode is between 1.91 W/cm² and3.18 W/cm² per unit surface area of the substrate, and the resistpattern is ashed by the plasma of the oxygen gas; and a recovering stepfollowing to the ashing step, in which an organic gas is supplied to thelow dielectric constant film so as to recovery of a damage of the lowdielectric constant film caused by the plasma.
 3. A storage mediumstoring a computer program operatable on a computer, wherein thecomputer program includes steps for performing the method ofmanufacturing a semiconductor device according to claim
 1. 4. A storagemedium storing a computer program operatable on a computer, wherein thecomputer program includes steps for performing the method ofmanufacturing a semiconductor device according to claim 2.